1. Field of the Invention
The present invention relates to pressure-sensing devices. More specifically, the present invention relates to an external fluid-filled catheter apparatus for sensing pressure in a fluid vessel in a living body.
2. Related Art
In the medical field, and particularly in the field of medical research, sensors greatly aid in the evaluation of performance and fluid characteristics of vessels in a living body. Sensors are used to determine characteristics such as fluid pressure, temperature, O2, CO2, sugar levels, and/or pH in blood vessels, lymph vessels, ureters, and ventricles. Medical personnel use this information to evaluate the overall health of a person, and medical researchers use this information to aid in the evaluation of new drugs or procedures.
Typically, sensors are mounted on a catheter for insertion into the vessel. Several patents describe the use of sensors mounted on catheters. However, the use of prior art catheters is not always possible due to the size of the vessel to be monitored in comparison with the catheter. For example, researchers studying cardiac performance in small animals such as mice may encounter blood vessels less than 1 mm in diameter. In these applications, it may not be possible, using prior art sensors, to be able to accurately monitor the cardiac performance directly. In particular, the size of the catheter may be so large that insertion into a blood vessel may block the blood vessel, impair cardiac performance, prevent accurate measurements, and cause injury to the subject. It is therefore desirable to provide an improved method and sensor apparatus for detecting fluid pressures in vessels in a living body. It is further desirable to provide a sensor apparatus capable of being used on small vessels.
In addition, the size of the catheter affects the measuring capability of the sensor. For example, the heart of a mouse beats at a very high rate. The volumetric displacement, however, is very small. If a large volume fluid-filled catheter is used to detect the blood pressure in a mouse blood vessel, the mouse heart may not be strong enough to provide the pressure needed to produce an accurate measurement in a large catheter. It is therefore desirable to provide a sensor apparatus that provides accurate measurements in applications with small volumetric displacement, small pressures, or high frequency pressure waveforms, or all three. It is further desirable to provide a fluid-filled catheter with a high-frequency response.
The present invention provides accurate measurement of fluid pressure with an inverted sensor module used with a fluid-filled catheter system. Such an invention provides a high-frequency response and allows for measurements in very small vessels less than one millimeter in diameter. The present invention also provides unique advantages relating to the modularity of the catheter pressure transducer.
In one broad respect, the present invention is directed to an external fluid-filled catheter transducer for sensing fluid pressures in body vessels in a living body, said external fluid-filled catheter transducer comprising: an inverted sensor module, said inverted sensor module comprising a sensor module carrier, a sensor mounted to said sensor module carrier such that the diaphragm of said sensor is positioned to measure fluid characteristics on the inside of said inverted sensor module, and communication media connected to said sensor, wherein said sensor is operable to send information to a monitoring device through said communication media; semi-rigid tubing connected to said inverted sensor module and capable of insertion into said living body; flexible tubing connected between said semi-rigid tubing and said inverted sensor module; a reservoir of fluid connected to said inverted sensor module; and a port in said external fluid-filled catheter pressure transducer capable of introducing a reference pressure to said sensor. In an alternative embodiment of the present invention, the external fluid-filled catheter pressure transducer further comprises clamps operable to block the passage of any fluid through any of said sections of flexible tubing. In other embodiments, the semi-rigid tubing comprises polyimide, the flexible tubing comprises transparent silicone rubber, and the inverted sensor carrier comprises rigid tubing. In another embodiment the distal tip of the semi-rigid tubing for insertion into a living body is less than 1 mm in diameter. In other embodiments, the semi-rigid tubing for insertion into a living body is less than 3 cm in length, and the external fluid-filled catheter pressure transducer is operable to be flushed periodically to prevent contamination or clogging by body fluids. In another embodiment, the inverted sensor is operable to detect fluid pressures.
In another broad respect, the present invention is directed to a method for using an external fluid-filled catheter pressure transducer comprising an inverted sensor module, to monitor a fluid pressure in a body vessel, said method comprising the steps of: obtaining an external fluid-filled catheter pressure transducer comprising an inverted sensor module and semi-rigid tubing; priming said external fluid-filled catheter pressure transducer such that substantially no air exists in said external fluid-filled catheter pressure transducer; calibrating said external fluid-filled catheter pressure transducer based on a reference pressure; inserting the distal end of semi-rigid tubing into a target vessel in said living body, wherein said inverted sensor module remains outside said living body; and measuring the fluid pressure present in said target vessel.
In another broad respect, the present invention is directed to a method of manufacturing an external fluid-filled catheter pressure transducer comprising an inverted sensor module, said method comprising the steps of: connecting a first section of tubing to a first end of said inverted sensor module, said first end hereinafter referred to as the distal end, said first section of tubing comprising flexible tubing and semi-rigid tubing; connecting a second section of tubing to a second end of the inverted sensor module, said second end hereinafter referred to as the proximal end, and said second section of tubing comprising flexible tubing and semi-rigid tubing; and connecting said second section of tubing to a fluid-filled reservoir wherein said second section of tubing is capable of introducing a reference pressure on fluid contained within said second section of tubing. In an alternative embodiment, the method further comprises the step of attaching clamps to first and second sections of flexible tubing such that any section or combination of sections may be opened or closed independently or in combination. In another alternative embodiment, the semi-rigid tubing in said first section of tubing is tapered. In yet another alternative embodiment the tapered semi-rigid tubing is drawn.
In a preferred embodiment of the present invention, a fluid-filled catheter with an inverted sensor module comprises a pressure sensor operable to provide a signal representative of fluid pressure.